Flights of Fancy: Leonardo's Flying Machines

by Gemma White

Have you ever wondered how a bird flies? Have you ever run around mimicking a bird, flapping your arms, willing yourself to take off? Leonardo did. Well, we're not sure that he actually ran around, although that is fun to imagine. But it was his love for birds that provided a major source of inspiration for his endeavor to master the art of human flight. He thought that to understand how a bird flies would provide the key that would enable man to take to the air.

So what did Leonardo learn from birds?

They Make It Look So Easy

Leonardo's study of birds was extensive and obsessive. Notebooks that he kept over many years show pages and pages of observations and drawings, detailing every aspect of a bird's flight. He made detailed anatomical drawings of a bird's body and wings. He observed the subtle movements of the wings in flight, the reaction of the wings against different wind conditions, and how a bird can drop from the sky and dive to the ground or remain stationary in the wind by using fine movements of its wings and tail. He also had the great insight to understand how a bird can achieve motion by exerting more pressure against the air than the air exerts against its body.

Leonardo also performed many experiments. He constructed models to test the effect of shifting the bird's center of gravity. He built replicas of birds' and bats' wings, experimenting with different materials to test what would be the best material for a full-scale flying machine.

Throughout all these vigorous investigations, Leonardo believed that “the bird is an instrument operating through mathematical laws, which instrument is in the capacity of man to be able to make with all the motions.” So he thought that by understanding the mathematics underlying a bird's movement, man could then mimic it and take to the air.

Oops…a Power Problem!

However, there was an important issue that Leonardo failed to address: How can man power a flying machine? Remember, this is in an age before the first engine, so all designs had to be powered by human strength. Leonardo observed that birds in flight had great reserves of strength. Birds could carry their own weight in prey—an eagle carrying a hare between its talons—and they also had enough power to double or triple their normal rate of speed in order to escape from a pursuer or dive to catch lunch. But Leonardo claimed that man had comparable reserves of strength in his legs, enough power to keep him in the air.

Using all his acquired knowledge, Leonardo set to the task of designing a flying machine. He thought it was possible to re-create specifically the way a bird flies, and even on a larger scale. Around 1485, he drew detailed plans for a human-powered ornithopter—an aircraft with flapping wings. This design had a wooden framework, with the pilot's seat located inside a shell-shaped vessel. From this vessel, the pilot would operate two large batlike wings, which had pulleys connected to stirrups that he moved with his feet. This original design had the pilot lying down, but subsequent drawings showed him sitting or standing upright. However, the key to all these designs was the use of the legs to provide maximum muscle power. The plane's tail would provide flight and landing stability.

Actually, Leonardo never built any of his designs. So…would they have been successful? Probably not!

What We Know Now

In order to fly, we must generate enough lift (upward motion). This is achieved by creating enough thrust or power (forward motion) to overcome the weight of the machine and the drag (friction) of the air—and this is where Leonardo became untied. Lift is generated by air flowing over an airfoil, be it a wing or a propeller. The shape of the airfoil causes air to flow over its two sides differently. The shape of the upper side of a wing causes air to flow over it at a lower pressure than it does across its underside. This pressure difference causes the wing to rise. Engines on planes push the wings forward so more air flows across them, creating more lift.

Even though Leonardo realized that power was essential to success, the machines he designed would have been too heavy for man himself to generate enough thrust to power. If he had based his design on a hawk's wing, he may have been able to build a glider, but he couldn't have propelled any design, no matter what the wing shape.

In fact, we had to wait another 400 years for our first powered flight—until 1903, when the Wright brothers successfully constructed an engine-powered plane that made human flying possible.

Is Man Strong Enough to Fly?

Here are Leonardo's thoughts on the subject:

“…place a man to stand upon the sea-shore, and observe how far the marks of his feet sink in; and then set another man on his back, and then you will see how much deeper the marks of his feet will be. Then take away the man from his back, and set him to jump straight up as high as he can; you will then find that the marks of his feet make a deeper impression where he has jumped than where he has had the other man on his back. This affords us a double proof that man is possessed of more than twice the amount of strength that is required to enable him to support himself.”

Isn't it interesting how Leonardo's mind worked?

Onward…and Upward

Leonardo eventually realized that his attempts to impose the mechanics of a bird's flight onto a man-made flying machine would never get off the ground, so he considered some alternatives:

“Leonardo's helicopter”—His most famous flying machine, this resembles a giant aerial screw. It is a framework with a spiral of fabric above it that whirls around to create lift. The idea never really took off.

Glider—Leonardo noticed that the inner part of a bird's wing moved more slowly than the outer. He concluded that the outer part of the wing was designed to keep a bird aloft rather than push it forward. Leonardo mimicked the design in his glider by having maneuverable tips at the end of the wings, controlled by straps attached to the pilot's legs and body. Seeing one of these would cause quite a flap today.

Parachute—Leonardo remarked that with a stiff linen curtain shaped into a pyramid with a base 11 meters across and equally deep, “anyone can jump from no matter what height without any risk whatsoever.”

With these designs, the legacy of Leonardo is very much evident in aircraft today. However, in his day and age, they left him grounded!

Vocabulary

Activity

What kind of power source did Leonardo indicate would power his flying machines?

Since the time of Leonardo, people have learned how to manufacture materials that are lightweight and strong. Using materials available today, what kinds of improvements might be made on Leonardo's flying machines? Do you think this would enable one of his designs to work? Choose Leonardo's helicopter, glider, or parachute design. Write a short paragraph describing what kinds of materials you would use to build this machine. Will the machine work with the new materials? Include details about why the machine would or would not work if it were made with modern materials.